Abstract: A cylindrical strand with a thermoplastic outer shell (e.g., plastic insulated wire) is bonded along its length to a similar or different cylindrical strand by laser heating. The strands are brought into contact with one another at a contact point. A laser beam of selected power and wavelength is directed at the contact point in a direction approximately parallel to the axis of the strands as the strands are carried past this point. Absorption of the light by the plastic causes melting sufficient to produce bonding. The depth of penetration of the thermal energy into the plastic is controlled by selection of the wavelength of the laser radiation relative to the absorption spectrum of the thermoplastic material. The laser power level is adjusted to control the total energy input in accordance with the strand feed rate.